How Soil Surveys Were Made
Over the years many landowners have wondered how and when soil types were
determined and how soil surveys were completed. The following should give a good idea of how
this seemingly insurmountable task was accomplished. Major fieldwork for the initial Athens
County Soil Survey was completed in 1980. Soil names and descriptions were approved in
1981.
Soil surveys were made to provide information about the soils in the survey area. The
information includes a description of the soils and their location and a discussion of the
suitability, limitations, and management of the soils for specified uses. Soil scientists observed
the steepness, length, and shape of slopes; the general pattern of drainage; the kinds of crops
and native plants growing on the soils; and the kinds of bedrock. They dug many holes to study
the soil profile, which is the sequence of natural layers, or horizons, in a soil. The profile extends
from the surface down into the unconsolidated material in which the soil formed. The
unconsolidated material is devoid of roots and other living organisms and has not been changed
by other biologic activity.
The soils in the survey area occur in an orderly pattern that is related to the geology, the
landforms, relief, climate, and the natural vegetation of the area. Each kind of soil is associated
with a particular kind of landscape or with a segment of the landscape. By observing the soils in
the survey area and relating their position to specific segments of the landscape, a soil scientist
develops a concept, or model, of how the soils were formed. Thus, during mapping, this model
enables the soil scientist to predict with considerable accuracy the kind of soil at a specific
location on the landscape.
Commonly, individual soils on the landscape merge into one another as their
characteristics gradually change. To construct an accurate soil map, however, soil scientists
must determine the boundaries between the soils. They can observe only a limited number of
soil profiles. Nevertheless, these observations, supplemented by an understanding of the soillandscape relationship, are sufficient to verify predictions of the kinds of soil in an area and to
determine the boundaries.
Soil scientists recorded the characteristics of the soil profiles that they studied. They
noted soil color, texture, size and shape of soil aggregates, kind and amount of rock fragments,
distribution of plant roots, acidity, and other features that enable them to identify soils. After
describing the soils in the survey area and determining their properties, the soil scientists
assigned the soils to taxonomic classes (units). Taxonomic classes are concepts. Each
taxonomic class has a set of soil characteristics with precisely defined limits. The classes are
used as a basis for comparison to classify soils systematically. The system of taxonomic
classification used in the United States is based mainly on the kind and character of soil
properties and the arrangement of horizons within the profile. After the soil scientists classified
and named the soils in the survey area, they compared the individual soils with similar soils in
the same taxonomic class in other areas so that they could confirm data and assemble
additional data based on experience and research.
While a soil survey is in progress, samples of some of the soils in the area generally are
collected for laboratory analyses and for engineering tests. Soil scientists interpreted the data
for these analyses and tests as well as the field-observed characteristics and the soil properties
in terms of expected behavior of the soils under different uses. Interpretations for all of the soils
were field tested through observation of the soils in different uses under different levels of
management. Some interpretations are modified to fit local conditions, and new interpretations
sometimes are developed to meet local needs. Data were assembled from other sources, such
as research information, production records, and field experience of specialists. For example,
data on crop yields under defined levels of management were assembled from farm records and
from field or plot experiments on the same kinds of soil.
Predictions about soil behavior are based not only on soil properties but also on such
variables as climate and biological activity. Soil conditions are predictable over long periods of
time, but they are not predictable from year to year. For example, soil scientists can state with a
fairly high degree of probability that a given soil will have a high water table within certain depths
in most years, but they cannot assure that a high water table will always be at a specific level in
the soil in a specific date.
After soil scientists located and identified the significant natural bodies of soil in the
survey area, they drew the boundaries of these bodies in aerial photographs and identified each
as a specific map unit. Aerial photographs show trees, buildings, fields, roads, and rivers, all of
which help in locating boundaries accurately.
Update! Although the footprint of our soil is unchanged, soil scientists continue to work
on updating soils descriptions to match surrounding counties and to develop more accurate
nomenclature for our soils naming system.